Cooling circuits using water, possibly with the addition of glycol, to cool a compressor of a stream rich in carbon dioxide are known from US-A-2011/0265477.
After a gas stream rich in carbon dioxide has been purified, it is often necessary to condense it so that it can be pumped to a pipeline.
In FIG. 1, a compressor 3 compresses a fluid 1 containing carbon dioxide at a pressure of 1 bar. The compressor is kept cold via a water circuit 5, 5A. The compressed fluid 7 is purified in a purification unit 9 and separated by separation means, in this instance a low-temperature distillation column 15. The fluid is cooled in the exchanger 13, condenses at least partially in a bottom reboiler 17 and is sent as feedstock to the column 15. The head gas 22 rich in light components is expanded in a turbine 24. The bottom liquid 19 vaporizes in the exchanger 13 to form a stream of gas rich in carbon dioxide which is compressed in a compressor 21. This compressor is cooled by a water circuit 23, 23A. The stream of gas at 60 bar is condensed by exchange of heat with a stream of water 31 to form the liquid 29 which is pumped in the pump 33 at a pressure greater than 110 bar to form the pressurized liquid product 35.
The book “Fabrication et Applications Industrielles de CO2 [Production and industrial applications of CO2]” by M. Vollenweider, published by Dunod, 1958, teaches how to use a water circuit in common for cooling the carbon dioxide that is to be condensed and for cooling the compressor of the carbon dioxide that is to be condensed. Now, FIG. 111-1 on page 30 shows two streams of water which are independent: the water used to condense the carbon dioxide is not used thereafter for cooling the compressor. The method in this Figure corresponds to the preamble of the first independent claim.
It is also often necessary to condense the gaseous stream rich in carbon dioxide so that it can be supercooled for use as a refrigeration cycle as illustrated in FIG. 2.
In this instance, a refrigeration cycle uses as its cycle gas a stream rich in carbon dioxide. This closed circuit comprises a condenser 27 cooled by a stream of water. The gas rich in carbon dioxide liquefies therein to form the stream 29, and the stream 29 is divided into four streams by the splitter 37. Each of the streams is expanded through a valve V1, V2, V3, V4 and is vaporized in the exchanger 13. The lowest-pressure stream is compressed in the compressor 121, another is compressed in the compressor 221 and three of the streams are combined before being compressed in the compressor 21. The fourth stream is introduced into the compressor 21 at an intermediate level, and the entire stream is sent to the condenser 27.
Another gas rich in carbon dioxide 1 is sent to a compressor 3, cooled in the exchanger 13, partially condensed and then sent to the first phase separator 39. The liquid 43 from the first phase separator 39 is expanded and sent to the top of a distillation column 15. The gas for the first phase separator is cooled in the exchanger 13, then sent to the second phase separator 41. The liquid 45 formed is expanded and sent to the top of the column 15. The gas 43 is heated up in the exchanger 13, expanded through two turbines 45, 48 then leaves as a stream 49. The liquid 19 from the bottom of the column is cooled in the exchanger 13 to form a liquid product at 7 bar and −50° C. The cold for this liquefaction is therefore supplied by the refrigeration cycle.
The head gas 47 of the column 15 is heated and sent to an intermediate level of the compressor 3.
The condensation temperature of the gaseous stream rich in carbon dioxide 25 defines the pressure to which the stream rich in carbon dioxide needs to be compressed in a compressor. The lower this temperature, the less compression energy is required, and the more economical the compressor.